1. Field of the Invention
The present disclosure relates to a method of reducing transmission power and a terminal thereof.
2. Discussion of the Related Art
Recently, studies on a next-generation multimedia radio communication system have been actively conducted. The radio communication system requires a system that can process various information including images, radio data, etc. in lieu of services mainly using voice and transmit the information. The object of the radio communication system enables a plurality of users to perform reliable communication regardless of location and mobility. However, wireless channels suffer from several problems such as path loss, shadowing, fading, noise, limited bandwidth, power limitation of terminals and inter-user interference. Other challenges in the design of the radio communication system include resource allocation, mobility issues related to rapidly changing physical channels, portability and design for providing security and privacy.
When a transmission channel suffers from deep fading, if another version or replica of a signal transmitted to a receiver is not separately transmitted to the receiver, it is difficult for a receiver to determine the transmitted signal. A resource corresponding the separate version or replica is called as a diversity, and the diversity is one of the most important factors contributing to reliable transmission. If the transmission capacity or transmission reliability of data can be maximized using the diversity, and a system for implementing a diversity using multiple transmit and receive antennas is referred to as a multiple input multiple output (MIMO) system.
Techniques for implementing the diversity in the MIMO system are space frequency block code (SFBC), space time block code (STBC), cyclic delay diversity (CDD), frequency switched transmit diversity (FSTD), time switched transmit diversity (TSTD), precoding vector switching (PVS), spatial multiplexing (SM), etc.
Meanwhile, one of systems considered after the 3rd generation system is an orthogonal frequency division multiplexing (OFDM) system capable of reducing an inter-symbol interference effect with low complexity. The OFDM system converts serially input data into N parallel data and transmits the N parallel data respectively carried by N orthogonal subcarriers. The subcarrier maintains orthogonality in terms of frequencies. Orthogonal frequency division multiple access (OFDMA) refers to Orthogonal Frequency Division Multiple Access (OFDMA) refers to a multiple access method of realizing multi-access by independently providing users with some of available subcarriers in a system using OFDM as a modulation method.
FIG. 1 illustrates a radio communication system.
Referring to FIG. 1, the radio communication system includes at least one base station (BS) 20. Each of the BSs 20 provides a communication service for a specific terrestrial area (generally, referred to as a cell) 20a, 20b or 20c. The cell may be divided into a plurality of areas (also referred to as sectors). A user equipment (UE) 10 may be fixed or have mobility. The UE 10 may be called as other terms including a mobile station (MS), a subscriber station (SS), a wireless device, a personal digital assistant (PDA), a wireless modem, a handheld device, etc. The BS 20 generally refers to a fixed station communicating with the UEs 10, and may be called as other turns including an evolved-NodeB (eNB), a base transceiver system, an access point, etc.
Hereinafter, downlink (DL) means communication from a BS to a UE, and uplink (UL) means communication from a UE to a BS. In the DL, a transmitter may be a portion of the BS and a receiver may be a portion of the UE. In the UL, a transmitter may be a portion of the UE and a receiver may be a portion of the BS.
The radio communication system may be any one of a multiple input multiple output (MIMO) system, a multiple input single output (MISO) system, a single input single output (SISO) system and a single input multiple output (SIMO). The MIMO system uses a plurality of transmit antennas and a plurality of receive antenna. The MISO system uses a plurality of transmit antennas and one receive antenna. The SISO system uses one transmit antenna and one receive antenna. The SIMO system uses one transmit antenna and a plurality of receive antennas.
Hereinafter, the transmit antenna means a physical or logical antenna used to transmit one signal or stream, and the receive antenna means a physical or logical antenna used to receive one signal or stream.
Meanwhile, a long term evolution (LTE) system defined by 3rd generation partnership project (3GPP) employs the MIMO. Hereinafter, the LTE system will be described in detail.
FIG. 2 illustrates a structure of a radio frame in 3GPP LTE.
Referring to FIG. 2, the radio frame is composed of ten subframes, and one subframe is composed of two slots. The slots in the radio frame are designated by slot numbers from 0 to 19. The time at which one subframe is transmitted is referred to as a transmission time interval (TTI). The TTI may be called as a scheduling unit for data transmission. For example, the length of one radio frame may be 10 ms, the length of one subframe may be 1 ms, and the length of one slot may be 0.5 ms.
The structure of the radio frame is merely an example, and the number of subframes included in the radio frame, the number of slots included in the subframe, etc. may be variously modified.
FIG. 3 is an exemplary view illustrating a resource grid for one UL slot in the 3GPP LTE.
Referring to FIG. 3, the UL slot includes a plurality of OFDM symbols in a time domain, and includes NUL resource blocks (RBs) in a frequency domain. The OFDM symbol is used to represent one symbol period, may be called as an SC-FDMA symbol, OFDMA symbol or symbol period depending on a system. The BS includes a plurality of subcarriers in the frequency domain as a resource allocation unit. The number NUL of RBs included in the UL slot depends on the UL transmission bandwidth configured in a cell. Each element on a resource grid is referred to as a resource element.
Although it has been illustrated in FIG. 3 that one RB includes a 712 resource element composed of 7 OFDM symbols in the time domain and 12 subcarriers in the frequency domain, the number of subcarriers and the number of OFDM symbols in the RB are not limited thereto. The number of OFDM symbols and the number of subcarriers in the RB may be variously changed. The number of OFDM symbols may be changed depending on the length of a cyclic prefix (CP). For example, the number of OFDM symbols in a normal CP is 7, and the number of OFDM symbols in an extended CP is 6.
The resource grid for one UL slot in the 3GPP LTE of FIG. 3 may be applied to the resource grid for one DL slot.
FIG. 4 illustrates a structure of a DL subframe.
The DL subframe includes two slots in the time domain, and each of the slots includes seven OFDM symbols in the normal CP. Maximum three OFDM symbols (maximum four OFDM symbols for a bandwidth of 1.4 MHz) prior to a first slot in the subframe become a control region to which control channels are allocated, and the other OFDM symbols become a data region to which a downlink shared channel (PDSCH) is allocated. The PDSCH means a channel through which a BS transmits data to a UE.
A physical downlink control channel (PDCCH) may carry resource allocation (also referred to as DL grant) and transmission format on a downlink-shared channel (DL-SCH), resource allocation information (also referred to as UL grant) on a uplink-shared channel (UL-SCH), paging information on a paging channel (PCH), system information on the DL-SCH, resource allocation of an upper layer control message such as a random access response transmitted on the PDSCH, a set of transmission power control (TPC) for individual UEs in a UE group, activation of a voice over Internet protocol (VoIP), etc. The control information transmitted through the PDCCH as described above is referred as downlink control information (DCI).
FIG. 5 illustrates an example of the structure of the uplink subframe in the 3GPP LTE.
Referring to FIG. 5, the uplink subframe may be divided into a control region in which a physical uplink control channel (PUCCH) carrying uplink control information is allocated and a data region in which a physical uplink shared channel (PUSCH) carrying uplink data information is allocated. To maintain a single carrier property, RSs allocated to one UE are contiguous in the frequency domain. The one UE cannot transmit the PUCCH and the PUSCH at the same time.
The PUCCH for one UE is allocated as an RB pair in a subframe. RBs constituting the RB pair occupy different subcarriers in first and second slots, respectively. The frequency occupied by each of the RBs constituting the RB pair is changed at a boundary between the slots. The UE transmits uplink control information through different subcarriers according to time, thereby obtaining a frequency diversity gain.
The uplink control information transmitted on the PUCCH includes hybrid automatic repeat request (HARQ) acknowledgement (ACK)/negative acknowledgement (NACK), channel quality indicator indicating a downlink channel state, scheduling request (SR) that is an uplink radio resource allocation request, etc.
The PUSCH is mapped to the UL-SCH that is a transport channel. Uplink data transmitted on the PUSCH may be a transport block that is a data block for the UL-SCH transmitted for the TTI. The transport block may be user information, or the uplink data may be multiplexed data. The multiplexed data may be data obtained by multiplexing the transport block for the UL-SCH and control information. For example, the control information multiplexed by the data may include CQI, PMI, HARQ ACK/NACK, RI, etc. The uplink data may be composed of only the control information.
Meanwhile, a high data transmission rate is required, and the most general and stable plan for solving the high data transmission rate is to increase a bandwidth.
However, frequency resources are currently in a saturation state, various technologies are partially used in a wide frequency band. For this reason, carrier aggregation (CA) has been introduced as a plan for securing a wideband bandwidth in order to satisfy the requirement of the high data transmission rate. Here, the CA is a concept of designing to satisfy general requirements that an independence system is operable in each of the scattered bands and binding a plurality of bands using one system. In the CA, the band in which the independent system is operable is defined as a component carrier (CC).
The CA is employed not only in the LTE system but also in the LTE-advanced (hereinafter, referred to as an ‘LTE-A’) system.
Carrier Aggregation
A carrier aggregation system refers to a system that forms a wide band by aggregating one or more carriers having a bandwidth narrower than a desired wideband when a radio communication system intends to support the wideband. The carrier aggregation system may be called as other terms including a multiple carrier system, a bandwidth aggregation system, etc. The carrier aggregation system may be divided into a contiguous carrier aggregation system in which carriers are contiguous and a non-contiguous carrier aggregation system in which carriers are separated from one another. Hereinafter, when the carrier aggregation system is simply called as a multiple carrier system or carrier aggregation system, it should be understood that the carrier aggregation system includes both cases in which component carriers are contiguous and in which component carriers are non-contiguous.
In the contiguous carrier aggregation system, a guard band may exist between carriers. When one or more carriers are aggregated, the carriers to be aggregated may use the bandwidth used in a conventional system as it is for the purpose of backward compatibility with the conventional system. For example, the 3GPP LTE system supports bandwidths of 1.4 MHz, 3 MHz, 5 MHz, 10 MHz, 15 MHz and 20 MHz. Alternatively, the 3GPP LTE does not use the bandwidth used in the conventional system as it is but may form a wideband by defining a new bandwidth.
In the carrier aggregation system, the UE may simultaneously transmit or receive one or a plurality of carriers according to its capacity.
FIG. 6 illustrates an example of performing communication under a single component carrier situation. FIG. 6 may correspond to an example of performing communication in an LTE system.
Referring to FIG. 6, a general frequency division duplex (FDD) radio communication system transmits/receives data through one downlink band and one uplink band corresponding thereto. The BS and the UE transmits/receive data and/or control information scheduled as a subframe unit. The data is transmitted/received through the data region configured in the uplink/downlink subframe, and the control information is transmitted/received through the control region configured in the uplink/downlink subframe. To this end, the uplink/downlink subframe carries signals through various physical channels. Although the FDD radio communication system has been mainly described in FIG. 6, the aforementioned description may be applied to a time division duplex (TDD) radio communication system by dividing a radio frame into uplink/downlink radio frames in the time domain.
FIG. 7 illustrates an example of performing communication under a multiple component carrier situation. FIG. 7 may correspond to an example of performing communication in an LET-A system.
The LTE-A system uses a carrier aggregation or bandwidth aggregation using a wider uplink/downlink bandwidth by aggregating a plurality of uplink/downlink frequency blocks so as to use a wider frequency band. Each of the frequency blocks is transmitted using a component carrier (CC). In this specification, the CC may mean a frequency block for carrier aggregation or a central carrier of the frequency block according to the context, and the frequency block and the central carrier are used together.
On the other hand, the 3GPP LTE system supports a case in which the uplink/downlink bandwidths are configured differently, but supports one CC in each of the uplink/downlink bandwidths. The 3GPP LTE system supports a maximum bandwidth of 20 MHz, and supports only one CC in each of the uplink/downlink bandwidths. Here, the uplink/downlink bandwidths may be different from each other.
However, the spectrum aggregation (bandwidth aggregation or carrier aggregation) supports a plurality of CCs. For example, if five CCs are allocated as the granularity of a carrier unit having a bandwidth of 20 MHz, the spectrum aggregation can support a maximum bandwidth of 100 MHz.
A pair of DL CC or UL CC and DL CC may correspond to one cell. The one cell generalally includes one DL CC and optionally includes UL CC. Therefore, it may be considered that the UE communicating with the BS through a plurality of DL CCs receive services from a plurality of serving cells. The DL is composed of a plurality of DL CCs, but the UL may use only one CC. In this case, it may be considered that the UE receives services from a plurality of serving cells in the DL and receives a service from one serving cell in the UL.
In this meaning, the serving cell may be divided into a primary cell and a secondary cell. The primary cell operates at a primary frequency, and is used to perform an initial connection establishment process, connection re-establishment process or handover process of the UE. The primary cell is also referred to as a reference cell. The secondary cell operates at a secondary frequency, and may be configured after RRC connection is established. The secondary cell may be used to provide an additional radio resource. At least one primary cell is always configured, and the secondary cell may be added/modified/cancelled by upper layer signaling (e.g., an RRC message).
Referring to FIG. 7, five CCs having a bandwidth of 20 MHz may be aggregated in each of the UL/DL, thereby supporting a bandwidth of 100 MHz. CCs may be adjacent or non-adjacent to one another in the frequency domain. For convenience, FIG. 9 illustrates a case in which the bandwidths of UL and DL CCs are identical and symmetric to each other. However, the bandwidth of each of the CCs may be independently determined. For example, the bandwidth of the UL CC may be configured as 5 MHz (UL CC0)+20 MHz (UL CC1)+20 MHz (UL CC2)+20 MHz (UL CC3)+5 MHz (UL CC4). Asymmetric carrier aggregation may be implemented in which the number of UL CCs is different from that of DL CCs. The asymmetric carrier aggregation may be formed due to limitation of an available frequency band or may be artificially formed by network configuration. For example, although the frequency band of the entire system is composed of N CCs, the frequency band received by a specific UE may be limited to M(<N) CCs. Various parameters for the CA may be configured in a cell-specific, UE group-specific or UE-specific manner.
Although it has been illustrated in FIG. 7 that the UL and DL signals are respectively transmitted through CCs mapped one by one, the CC through which a signal is substantially transmitted may be changed depending on the network configuration or kind of signal.
For example, when a scheduling command is downlink-transmitted through the DL CC1, data according to the scheduling data may be transmitted through another DL CC or UL CC. Control information related on the DL CC may be uplink-transmitted through a specific UL CC regardless of the presence of mapping. Similarly, DL control information may also be transmitted through a specific DL CC.
FIG. 8 illustrates a usage example of Band 13 defined in the LTE system when the Band 13 is used in U.S.A. Here, the Band 13 refers to a frequency band having a DL bandwidth of 746 to 756 MHz and a UL bandwidth of 777 to 787 MHz.
Referring to FIG. 8, as the frequency policies for each country and for each region are separately established, there occurs a case where an adjacent frequency band of the frequency band used by terminals should be protected for each country and for each region. As can be seen in FIG. 8, a frequency band for public safety in an adjacent band of the Band 13, i.e., a public safety (PS) band is specified in U.S.A, and interface in the PS band, caused due to another system, is restricted to a certain numerical value or less.
However, if frequency bands in the LTE system are placed as shown in FIG. 8, and each UE transmits a signal using general power, the transmitted signal cannot satisfy requirements for emission specified in the corresponding country.
That is, if a signal is transmitted in the Band 13, unwanted emission occurs in an adjacent band. Therefore, the adjacent band is interfered due to the unwanted emission.